ARS scientist tells why

Soil `amendments' may keep soil on farm EVER NOTICE there's less dust a-flying when cropland is plowed during the winter months compared to when the same land might be plowed during the summer time?

There's a reason for it. and there's a lot more to it than simply the amount of moisture that may be present in the soil at the time the land is tilled, says a USDA soil scientist.

Dr. Ted M. Zobeck of Lubbock says, yes, while moisture, temperature and wind speed are critical factors in soil movement, a number of other conditions can influence the degree of dustiness mobility of the soil as well. A change in soil structure within a single year - or actually over a few months - may also be a factor.

It is a known fact that the level of "dustiness" coming from a cultivated field when it is plowed is a direct indicator of how blowing wind and falling rain may impact a land resource in terms of these two economically important kinds of soil erosion.

Zobeck, who is with the USDA-Agricultural Research Service's Cropping Systems Research Laboratory, is leading a wide-ranging study into soil particle aggregation - and how various soil amendments might help stabilize the soil and, thus, reduce costly soil erosion losses for farmers. His work is targeted at some of the more highly-erodible sandy loam cropland soils from both the Texas Plains and Mississippi.

The Texas soils being studied generally carry an organic matter (OM) content of no more than eight-tenths of one percent.

"Tillage and oxidation are two important reasons that soil organic matter gets away so fast from sandy loam soils compared to clay soil types," Zobeck explains. "When the basic structure breaks down, you have a low stability soil." Various mineral and chemical components within the soil join together with any available organic matter (from crop residues) and living microbes to set up a condition that works together to form the desired particle structure system within a soil - actually in any soil.

"But we know that tillage, water and wind tends to break down that structure, particularly in sandy loam soils, quickly."

A soil sample dug out of a native prairie grassland, for example, may have many, many BB-sized soil particles or aggregates in it, reflecting its very good structure. That would compare to a low organic matter that, with water added, runs together and crusts over rapidly in what is called a "puddled state." A moderate to high OM content is desired in any soil.

One encouraging soil amendment that Zobeck is working with - and has reported on in the scientific journals - is ferrihydrite, a high-iron compound. Ferrihydrite is a by-product of wastewater treatment, and would be inexpensive to use. It might be added to commercial fertilizers. There are no commercial sources of ferrihydrite available in the United States currently. But Zobeck's results with "dustiness" reduction in the test soils in the laboratory are promising.

An improvement in a soil's structure can mean, he points out, better general "workability" of the soil, improved soil water-holding capacity, and reduced wind and water erosion potential, including reduced levels of surface crusting.

All this might mean Texas Plains farmers would spend less time on their sand fighters each April and May when high winds normally blow across the region.

"We are trying today to see how this amendment applied at various rates will modify the soil's structure and increase particle aggregation," he explains. Zero, 300, 3000 and 30,000 pounds per acre equivalents of the iron-laden material have been applied to the soil - but only under laboratory conditions so far. He and his associates are ready to take their work out into the field.

His initial lab studies have discovered that the lowest-level 300 pounds per acre of ferrihydrite is as effective in reducing levels of dust coming from such soils as the higher treatment levels. Results are based on nine drying and wetting cycles of soils treated with the various levels of product and without ferrihydrite as a control check. Some very sophisticated laboratory equipment to measure dustiness has been devised and is being used.

"To me, the dustiness of a soil is a measure of how soils break down in cultivation." With the use of 300 pounds per acre of ferrihydrite, the dust levels of warm-season soils have been greatly reduced.

Specifically, the scientist reports, there is three times as much dust coming from warm-season conditioned soils than from cool-season conditioned soils (same soil). With ferrihydrite applied (300 pounds per acre equivalent) dustiness in warm-season conditioned soil was reduced to one-third of the control warm-season conditioned soils.

The next step in the laboratory, Zobeck says, is to investigate the effects of even lower levels of the product and fewer wetting and drying cycles on the amount of dust emitted from a wider number of soil types.

While soil amendments carry something of a negative connotation in the minds of some farmers, Zobeck reminded that so-called amendments can be a wide array of commonly used products. "Fertilizers, for example," Zobeck said, "are amendments."